QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1289 NO RSENSE STEP-DOWN DC/DC CONVERTER LTC3879EUD DESCRIPTION Demonstration circuit 1289 is a no rsense step-down dc/dc converter featuring the LTC3879EUD. Its output supplies 1.2V @ 15A and its input voltage range is from 4.5V to 14V. The demo board uses a high density, two sided drop-in layout. The power components, excluding the bulk output capacitors and bulk input capacitors, fit within a 0.94” x 0.69” area on the top layer. The control circuit on the bottom layer has a footprint of 0.40” x 0.50”. The fixed on-time valley current mode architecture of the LTC3879EUD provides a very fast load step response. Other features of the board include a RUN pin, a TRACK pin, a PGOOD pin and a MODE jumper to select either CCM or DCM operation at light load. Design files for this circuit board are available. Call the LTC factory. Table 1. Performance Summary (TA = 25°C) PARAMETER CONDITION VALUE Minimum Input Voltage 4.5V Maximum Input Voltage 14V Output Voltage VOUT VIN = 4.5V to 14V, IOUT = 0A to 15A 1.2V ±2% Maximum Output Current 15A Typical Output Voltage Ripple VIN = 12V, IOUT = 15A (20MHz BW) 18mVP–P Nominal Switching Frequency 100% load 430kHz Efficiency (see Figure 3 for efficiency curves) VIN = 12V, 100% load 87.7% Typical QUICK START PROCEDURE Demonstration circuit 1289 is easy to set up to evaluate the performance of the LTC3879EUD. Refer to Figure 1 for proper measurement equipment setup and follow the procedure below: 1. NOTE: When 2. With power off, connect the input power supply to Vin and GND. 3. Turn on the power at the input. 4. Check for the proper output voltages. Vout = 1.176V to 1.224V 5. Once the proper output voltages are established, adjust the loads within the operating range and observe the output voltage regulation, ripple voltage, efficiency and other parameters. measuring the input or output voltage ripple, care must be taken to avoid a long ground lead on the oscilloscope probe. See Figure 2 for proper scope probe technique. Short, stiff leads should be soldered to the (+) and (-) terminals of an output capacitor. The probe’s ground ring needs to touch the (-) lead and the probe tip needs to touch the (+) lead. Place jumpers in the following positions: RUN ON MODE CCM 1 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1289 NO RSENSE STEP-DOWN DC/DC CONVERTER Figure 1. Proper Measurement Equipment Setup + COUT VOUT - GND Figure 2. Measuring Output Voltage Ripple 2 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1289 NO RSENSE STEP-DOWN DC/DC CONVERTER Fsw = 430kHz, CCM 95 Efficiency 90 85 80 Parameters: Qtop = RJK0305DPB Qbottom = RJK0330DPB L = Vishay IHLP4040DZ-01 0.36uH Ron = 402K Design optimized for a 12V input 75 70 0 2 4 6 8 10 12 14 16 Load current (Amps) Vin = 12V Vin = 5V Figure 3. Typical Efficiency Curves 3 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1289 NO RSENSE STEP-DOWN DC/DC CONVERTER 4